fix: audit round 3 deferred items (S1, C2) - #28
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S1 (LOW, defense-in-depth): AuthManager::is_valid now compares the session token against every stored entry in constant time (subtle::ConstantTimeEq), so validation latency does not leak how much of a guessed token matched. Tokens are 48 random alphanumeric chars behind a SipHash-keyed HashMap, so this is hardening rather than a practical fix, but it keeps the auth gate branch-free. C2 (reachable, reclassified from dormant): SerialPane::spawn is wired into Window::add_serial_pane, so serial panes are live. Previously make_full_refresh returned a blank grid and pre-attach output was lost, leaving serial panes blank until the next byte. Mirror the PTY Pane snapshot design: the reader maintains a latest_grid via Grid::apply_dirty_row, and serial panes are now threaded through the attach and lag-resync full-refresh paths via Window::focused_pane_full_refresh / all_full_refreshes. DA/DSR write-back is intentionally not added (serial devices lack the PSReadLine handshake). Tests: existing auth adversarial tests cover the constant-time path; cargo test (267 passed) / clippy -D warnings / fmt --check green. Generated with [Claude Code](https://claude.ai/code) via [Happy](https://happy.engineering) Co-Authored-By: Claude <noreply@anthropic.com> Co-Authored-By: Happy <yesreply@happy.engineering>
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Addresses two deferred findings from the round 3 audit (docs/plans/audit-round3-2026h2.md).
S1 — constant-time session token comparison (LOW, defense-in-depth)
AuthManager::is_validcompared the token via aHashMaplookup. It now compares against every stored entry withsubtle::ConstantTimeEq, so validation latency does not reveal how much of a guessed token matched. Tokens are 48 random alphanumeric chars behind a SipHash-keyed map, so this is hardening rather than a practical fix, but it keeps the auth gate branch-free.C2 — serial pane blank-grid bug (reachable, reclassified)
SerialPane::spawnis wired intoWindow::add_serial_pane, so serial panes are live — C2 is not dormant. Previouslymake_full_refreshreturned a blank grid and any output emitted before a client attached was dropped (broadcast has no receivers), leaving the pane blank until the next byte.Fix mirrors the PTY
Panesnapshot design (v1.9.3):latest_gridviaGrid::apply_dirty_row(the P1 incremental pattern).Window::focused_pane_full_refresh(attach, serial-aware) andWindow::all_full_refreshes(P4 resync, includes serial).DA/DSR write-back is intentionally not added — serial devices lack the PSReadLine handshake that required it for ConPTY.
Tests
cargo test -p nexterm-server(267 passed),cargo clippy --all-targets -- -D warnings,cargo fmt --checkall green.Remaining deferred
P3, P6 (need profiling), P5, R5/A5 (require a
PROTOCOL_VERSIONbump), P7 (large lock-architecture refactor) stay tracked in the audit report.